The dialog box illustrated below is used to quantify whether or not each part of the watershed is suitable for its designated uses.
Each designated use in the watershed should have one or more water quality criteria. To add a criterion, click on the Add button. To select a criterion, choose the criterion number. For each criterion, select the parameter, then the numerical criterion. Select whether the criterion is based on a minimum or maximum value, the duration and type of average, whether it should be above or below the specified value, the numerical value itself, and the percent of the time the criterion must be met in order to meet the standard.
For example, anadromous fish might need dissolved oxygen of at least 7 mg/L. Click on Add to add the first criterion. Choose the “Dissolved Oxygen, mg/l” parameter from the list. Select “minimum” since the lowest dissolved oxygen concentration should be above 7. Select the number of days in the average which reflects whether the criterion is chronic or acute. For a chronic criterion, select several days, such as a 4 or 7-day average. Select “arithmetic” as the type of average (geometric is primarily used for fecal coliform criteria) and select “above” since dissolved oxygen should be higher than 7 mg/l to be acceptable. Enter “7” after “is above” to indicate the numerical criterion. Then select how often the criterion must be met. For example, if the criterion may be exceeded once every three years, enter “99.91” percent, which is approximately one day in 1,095.
Additional criteria can be added by clicking on Add. Note that criterion #2 is now ready to be edited. For example, select the Temperature parameter, “maximum”, the number of days to be averaged, “arithmetic”, “below”, 15 degees for the value, and the required compliance.
Another example is the swimmable criterion. State health requirements might indicate that waters are considered swimmable if fecal coliform levels are below 200 / 100 ml. Select “Fecal Coliform, #/100 ml”, “maximum”, 30 day average, “geometric” mean, “below”, 200 for the value, and the required compliance.